JP2009043776A - R-fe-b-based rare-earth sintered magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an R-Fe-B-based rare-earth sintered magnet which effectively uses a heavy rare earth element as a rare resource and whose consumption is reduced. <P>SOLUTION: In the manufacturing method of the R-Fe-B-based rare-earth sintered magnet, a bulk body 2 containing the heavy rare earth element RH (at least one selected from a group of Dy, Ho, and Tb) is disposed in a treatment chamber 11, which is then heated at 700 to 1,100°C to form an RH steam atmosphere at least in the vicinity of the bulk body 2 in the treatment chamber 11. Then an R-Fe-B-based rare earth sintered magnet body 1 is carried in the treatment chamber 11 and held for 10 to 600 minutes while arranging the R-Fe-B-based rare earth sintered magnet body 1 opposed to the bulk body 2. Thus, the heavy rare earth element RH is diffused into the sintered magnet body 1 while supplying the heavy rare earth element RH to the surface of the sintered magnet body 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an R—Fe—B rare earth sintered magnet having R ₂ Fe ₁₄ B type compound crystal grains (R is a rare earth element) as a main phase and a method for producing the same, and in particular, to a light rare earth element RL (Nd and Pr). At least one selected from the group consisting of heavy rare earth elements RH (at least one selected from the group consisting of Dy, Ho, and Tb). The present invention relates to a R-Fe-B rare earth sintered magnet and a method for producing the same.

R-Fe-B rare earth sintered magnets with Nd ₂ Fe ₁₄ B type compound as the main phase are known as the most powerful magnets among permanent magnets, and are voice coil motors (VCM) for hard disk drives. In addition, it is used in various motors such as motors for mounting on hybrid vehicles, and home appliances. When R-Fe-B rare earth sintered magnets are used in various devices such as motors, they are required to have excellent heat resistance and high coercive force characteristics in order to cope with high temperature use environments.

As a means for improving the coercive force of an R—Fe—B rare earth sintered magnet, an alloy prepared by melting and melting heavy rare earth element RH as a raw material is used. According to this method, since the rare earth element R in the R ₂ Fe ₁₄ B phase containing the light rare earth element RL as the rare earth element R is replaced with the heavy rare earth element RH, the magnetocrystalline anisotropy of the R ₂ Fe ₁₄ B phase ( The essential physical quantity that determines the coercivity is improved. However, the magnetic moment of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is in the same direction as the magnetic moment of Fe, whereas the magnetic moment of the heavy rare earth element RH is opposite to the magnetic moment of Fe. Therefore, as the light rare earth element RL is replaced with the heavy rare earth element RH, the residual magnetic flux density _Br decreases.

  On the other hand, since the heavy rare earth element RH is a rare resource, it is desired to reduce the amount of use thereof. For these reasons, the method of replacing the entire light rare earth element RL with the heavy rare earth element RH is not preferable.

By adding a relatively small amount of heavy rare earth element RH, the effect of improving the coercive force due to heavy rare earth element RH is exhibited, so that powders of alloys / compounds containing a lot of heavy rare earth element RH contain a lot of light rare earth element RL. It has been proposed to add it to the main phase mother alloy powder and form and sinter it. According to this method, since that would heavy rare-earth element RH is distributed more in the vicinity of grain boundaries of the R ₂ Fe ₁₄ B phase, efficiently magnetocrystalline anisotropy of the R ₂ Fe ₁₄ B phase in the outer periphery of the main phase It becomes possible to improve. Since the coercive force generation mechanism of the R-Fe-B rare earth sintered magnet is a nucleation type (nucleation type), a large amount of heavy rare earth elements RH are distributed in the main phase shell (near the grain boundary). The crystal magnetic anisotropy of the entire crystal grains is increased, and the nucleation of the reverse magnetic domain is prevented. As a result, the coercive force is improved. Further, since the substitution with the heavy rare earth element RH does not occur at the center of the crystal grains that do not contribute to the improvement of the coercive force, it is possible to suppress the decrease in the residual magnetic flux density _Br .

  However, when this method is actually carried out, the diffusion rate of the heavy rare earth element RH increases in the sintering process (executed at 1000 ° C. to 1200 ° C. on an industrial scale). As a result, it is difficult to obtain the expected structure.

  Further, as another means for improving the coercive force of the R—Fe—B rare earth sintered magnet, a metal, alloy, compound, or the like containing heavy rare earth element RH is deposited on the magnet surface at the stage of the sintered magnet, and then heat treated and diffused. Thus, it has been studied to recover or improve the coercive force without significantly reducing the residual magnetic flux density (Patent Document 1, Patent Document 2, and Patent Document 3).

  Patent Document 1 discloses that a thin film layer made of R ′ (R ′ is at least one of Nd, Pr, Dy, Ho, and Tb) is formed on a surface to be ground of a sintered magnet body, and then a vacuum or an inert atmosphere. It is disclosed that, by performing heat treatment, the altered layer on the ground surface is made a modified layer by the diffusion reaction between the thin film layer and the altered layer, and the coercive force is recovered.

  Patent Document 2 states that a metal element R (the R is a rare earth element selected from Y and Nd, Dy, Pr, Ho, and Tb) exceeds the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the small magnet. (1 type or 2 types) is diffused while forming a film, thereby modifying the damaged part of the work and improving (BH) max.

  In Patent Document 3, by forming a chemical vapor deposition film mainly composed of a rare earth element on the surface of a magnet having a thickness of 2 mm or less and then performing a heat treatment, the rare earth element diffuses inside the magnet, and the work deterioration layer near the surface is modified. It is disclosed that the magnetic properties are restored.

  Patent Document 4 discloses a rare earth element sorption method in order to recover the coercive force of an R—Fe—B micro sintered magnet or powder. In this method, a sorption metal (a rare earth metal having a relatively low boiling point such as Yb, Eu, Sm) is mixed with an R—Fe—B micro-sintered magnet or powder and then heated uniformly in a vacuum with stirring. A heat treatment is performed. By this heat treatment, the rare earth metal is deposited on the magnet surface and diffuses inside. Patent Document 4 also describes an embodiment in which a rare earth metal having a high boiling point (for example, Dy) is sorbed. In the embodiment using Dy or the like, Dy or the like is selectively heated to a high temperature by a high frequency heating method. For example, the boiling point of Dy is 2560 ° C., and Yb having a boiling point of 1193 ° C. is 800 to 850 ° C. It is considered that Dy is heated to a temperature exceeding at least 1500 ° C. because it is not heated sufficiently by normal resistance heating. Furthermore, it is described that the temperature of the R—Fe—B-based fine sintered magnet and the powder is preferably maintained at 700 to 850 ° C.

In Patent Document 5, a metal vapor atmosphere is formed by evaporating a metal evaporation material such as Dy or Tb in a processing chamber, and an R—Fe—B sintered magnet held at a temperature lower than the temperature in the processing chamber is carried into the processing chamber. In addition, a method is disclosed in which a metal evaporation material is selectively attached and deposited on the surface of the magnet due to a temperature difference between the processing chamber and the magnet, and then is carried out of the processing chamber and heated in a separate chamber for diffusion treatment.
Japanese Patent Laid-Open No. 62-074048 JP 2004-304038 A JP 2005-285859 A JP 2004-296773 A WO2006 / 100968 International Publication Pamphlet

In all of the conventional techniques disclosed in Patent Document 1, Patent Document 2, and Patent Document 3, a rare earth metal film is formed on the surface of the sintered magnet body, and the rare earth metal is diffused into the magnet by heat treatment. As a result, in the magnet surface layer region (region from the surface to a depth of several tens of μm), the rare earth metal is in the main phase with a large concentration difference in the rare earth metal concentration at the interface between the rare earth metal film and the sintered magnet body as the driving force. In other words, the residual magnetic flux density _Br is reduced.

In the prior art disclosed in Patent Document 4, since the film is formed by heating to a temperature at which rare earth metals such as Dy are sufficiently vaporized, the film formation rate is higher than the diffusion rate in the magnet. Is overwhelmingly high, and a thick Dy film is formed on the magnet surface. As a result, in the same manner as in Patent Documents 1 to 3, in the magnet surface layer region, Dy cannot be prevented from diffusing into the main phase, and the residual magnetic flux density _Br decreases.

  Also, since both the sorption raw material and the magnet are heated by high frequency, it is not easy to heat only the rare earth metal to a sufficient temperature and maintain the magnet at a low temperature that does not affect the magnetic properties. It is limited to a powder state that is difficult to be induction-heated or a very small one.

  Furthermore, in the methods of Patent Documents 1 to 4, since a large amount of rare earth metal is deposited on portions other than the magnet inside the apparatus (for example, the inner wall of the vacuum chamber) during the film forming process, resource saving of heavy rare earth elements, which are valuable resources, is saved. It will be contrary to the conversion.

In the method of Patent Document 5, since Dy, Tb, and the like are selectively deposited only on the surface of the magnet, it is said that Dy, Tb, etc., which are scarce in resources and can be effectively used. However, in the method of Patent Document 5, a processing chamber in which a metal evaporation material such as Dy or Tb is disposed is heated to 1000 ° C. or more to form a saturated atmosphere of the metal evaporation material, and a magnet is generated by the temperature difference between the vapor atmosphere and the magnet. After forming a thick film of a metal evaporation material on the surface in a short time (1 minute in the embodiment), it is taken out from the processing chamber and separately subjected to a diffusion treatment. Similarly, in the magnet surface layer region, it is inevitable that Dy diffuses into the main phase, and the residual magnetic flux density _Br decreases.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to reduce the residual magnetic flux density by suppressing the heavy rare earth element RH from diffusing within the main phase crystal grains. An object of the present invention is to provide an R—Fe—B rare earth sintered magnet having an improved coercive force with almost no decrease and a method for producing the R—Fe—B rare earth sintered magnet.

  Another object of the present invention is to effectively utilize a rare earth element RH, which is a rare resource, in an R—Fe—B based rare earth sintered magnet and reduce the amount of the rare earth element RH.

  In the method for producing an R—Fe—B rare earth sintered magnet of the present invention, a bulk body containing a heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) is disposed in a processing chamber. Then, the process chamber is heated to 700 ° C. or more and 1100 ° C. or less to form an RH vapor atmosphere at least in the vicinity of the bulk body in the process chamber, and an R—Fe—B system in the process chamber The step (B) of carrying in the rare earth sintered magnet body, and the R-Fe-B rare earth sintered magnet body facing the bulk body and holding for 10 minutes to 600 minutes, thereby holding the heavy A step of diffusing the heavy rare earth element RH into the R-Fe-B rare earth sintered magnet body while supplying the rare earth element RH to the surface of the R-Fe-B rare earth sintered magnet body (C) Including.

  In preferable embodiment, in the said process (C), the average space | interval of the said bulk body and the said R-Fe-B type rare earth sintered magnet body is set in the range of 0.1 mm or more and 300 mm or less.

  In preferable embodiment, in the said process (C), the temperature of the said bulk body and the said R-Fe-B type rare earth sintered magnet body is hold | maintained in the range of 700 degreeC or more and 1100 degrees C or less for 10 minutes-600 minutes.

In a preferred embodiment, in the step (C), the pressure of the atmospheric gas in the processing chamber is adjusted within a range of 10 ^{−5 to} 500 Pa.

  In a preferred embodiment, in the step (C), the temperature difference between the temperature of the R—Fe—B rare earth sintered magnet body and the temperature of the bulk body is kept within 20 ° C. for 10 minutes to 600 minutes. .

  In a preferred embodiment, before performing the step (B), a step of heating the R-Fe-B rare earth sintered magnet body in advance is performed.

  The R—Fe—B rare earth sintered magnet of the present invention is an R—Fe—B rare earth sintered magnet produced by any one of the above production methods.

  Another R—Fe—B rare earth sintered magnet according to the present invention includes an R—Fe—B rare earth sintered magnet containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R; And a film of heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) deposited on the surface of the R—Fe—B rare earth sintered magnet body. -Fe-B rare earth sintered magnet immediately after the heavy rare earth element RH film is deposited, the thickness of the film is 1 μm or less, and a part of the light rare earth element RL is heavy rare earth element Substituted by element RH.

  In the present invention, the heavy rare earth element RH is dispersed in the main phase by performing diffusion while supplying the heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) to the surface of the sintered magnet body. Since it is possible to suppress the intragranular diffusion inside the crystal grains, it is possible to obtain an R—Fe—B rare earth sintered magnet having an improved coercive force with almost no decrease in residual magnetic flux density. In addition, it is possible to realize a method for producing the R—Fe—B rare earth sintered magnet by effectively utilizing RH, which is a scarce resource, and reducing the amount of use thereof.

  In the method for producing an R—Fe—B rare earth sintered magnet of the present invention, a bulk body of heavy rare earth element RH that is difficult to vaporize (sublimate) is placed in a processing chamber and heated to 700 ° C. or higher and 1100 ° C. or lower. After forming an RH vapor atmosphere at least in the vicinity of the bulk body in the chamber, an R—Fe—B rare earth sintered magnet is carried into the processing chamber and held for 10 to 600 minutes. As a result, the heavy rare earth element RH comes to the surface of the sintered magnet body, but since the temperature of the RH bulk body is 700 ° C. or higher and 1100 ° C. or lower, vaporization (sublimation) of the RH bulk body is caused by the growth rate of the RH film Therefore, the heavy rare earth element RH flying on the surface of the sintered magnet body diffuses quickly into the magnet body. The temperature range from 700 ° C. to 1100 ° C. is a temperature at which the vaporization (sublimation) of the heavy rare earth element RH hardly occurs or is relatively difficult to occur, but the diffusion of the rare earth element in the R—Fe—B rare earth sintered magnet is small. It is also an active temperature. For this reason, it becomes possible to promote the diffusion of grain boundaries into the magnet body preferentially rather than the heavy rare earth element RH flying on the magnet body surface forming a film on the magnet body surface.

  In this specification, it is easy to diffuse the heavy rare earth RH from the surface of the sintered magnet body to the inside while supplying the heavy rare earth RH from the heavy rare earth bulk body (RH bulk body) to the surface of the sintered magnet body. Sometimes referred to as “evaporation diffusion”. According to the present invention, the heavy rare earth element RH diffuses and penetrates into the magnet at a higher rate than the rate at which the heavy rare earth element RH diffuses into the main phase located near the surface of the sintered magnet body. Will go.

  Conventionally, it is considered that the vaporization (sublimation) of heavy rare earth elements RH such as Dy requires heating to a high temperature exceeding 1500 ° C., and heating at 700 ° C. or higher and 1100 ° C. or lower causes Dy on the surface of the magnet body. It was thought that it was impossible to precipitate. However, according to experiments by the present inventors, it was found that, contrary to the conventional prediction, it is possible to supply and diffuse heavy rare earth elements RH to rare earth magnets arranged oppositely even at 700 ° C. or higher and 1100 ° C. or lower.

In the conventional technique in which a heavy rare earth element RH film (RH film) is formed on the surface of the sintered magnet body and then diffused into the sintered magnet body by heat treatment, “intragranular diffusion” occurs in the surface layer region in contact with the RH film. It progresses remarkably and the magnet properties are deteriorated. In contrast, in the present invention, the temperature of the sintered magnet body is maintained at a level suitable for diffusion while supplying the heavy rare earth element RH to the surface of the sintered magnet body while keeping the growth rate of the RH film low. Therefore, the heavy rare earth element RH flying on the surface of the magnet body quickly penetrates into the sintered magnet body by grain boundary diffusion. Therefore, even in the surface region, preferentially than the "intragrain diffusion" occurs "grain boundary diffusion", suppressing reduction of the remanence B _r, thereby making it possible to effectively improve the coercive force H _cJ become.

Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type, if the magnetocrystalline anisotropy in the outer shell of the main phase is increased, a reverse magnetic domain is formed in the vicinity of the grain boundary phase in the main phase. As a result, the coercive force H _{cJ of the} entire main phase is effectively improved. In the present invention, since the heavy rare earth substitution layer can be formed on the outer shell of the main phase not only in the area close to the surface of the sintered magnet body but also in the area deep from the magnet surface, The coercive force H _{cJ of the} whole magnet is sufficiently improved. Therefore, according to the present invention, the amount of consumed heavy rare earth element RH can be diffused and penetrated at least into the sintered body, and the heavy rare earth element RH can be efficiently diffused in the outer shell portion of the main phase. There by forming a concentrated layer, it is possible to improve the coercivity H _cJ while suppressing a decrease in the residual magnetic flux density B _r.

As the heavy rare earth element RH to be replaced with the light rare earth element RL in the outer shell of the main phase, Dy is most preferable in consideration of easiness of vapor deposition diffusion, cost, and the like. However, the magnetocrystalline anisotropy of Tb ₂ Fe ₁₄ B is higher than the magnetocrystalline anisotropy of Dy ₂ Fe ₁₄ B, and is about three times as large as that of Nd ₂ Fe ₁₄ B. Therefore, when Tb is vapor-deposited, the coercive force can be improved most efficiently without reducing the residual magnetic flux density of the sintered magnet body. When Tb is used, it is preferable to perform vapor deposition diffusion at a high temperature and high vacuum, rather than using Dy.

  As is clear from the above description, in the present invention, it is not always necessary to add the heavy rare earth element RH at the stage of the raw material alloy. That is, a known R—Fe—B rare earth sintered magnet containing a light rare earth element RL (at least one of Nd and Pr) as a rare earth element R is prepared, and heavy rare earth element RH is diffused from the surface into the magnet. To do. In the case where only the conventional heavy rare earth layer is formed on the magnet surface, it is difficult to diffuse the heavy rare earth element RH deep inside the magnet even if the diffusion temperature is increased. By the grain boundary diffusion of the element RH, the heavy rare earth element RH can be efficiently supplied also to the outer shell portion of the main phase located inside the sintered magnet body. Of course, the present invention may be applied to an R—Fe—B based sintered magnet to which a heavy rare earth element RH is added at the stage of a raw material alloy. However, if a large amount of heavy rare earth element RH is added at the stage of the raw material alloy, the effects of the present invention cannot be fully achieved, so a relatively small amount of heavy rare earth element RH can be added.

  Next, a preferred example of the diffusion process according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a configuration example of a vapor deposition diffusion apparatus that can be suitably used in the present invention, and FIG. 2 is a diagram showing a planar configuration of the apparatus. FIG. 2 schematically shows a configuration in which the inside of the apparatus is seen through from above.

  The illustrated vapor deposition diffusion device includes two chambers, a preparation chamber 10 and a processing chamber 11. An opening / closing port 14 a that can be opened and closed is provided on the inlet side of the preparation chamber 10, and an opening and closing port 14 c that can be opened and closed is provided on the outlet side of the processing chamber 11. In addition, an opening / closing port 14 b that can be opened and closed is provided between the preparation chamber 10 and the processing chamber 11. These loading / unloading ports 14a, 14b, and 14c can be opened and closed independently. In the example shown in FIG. 1, since the carry-in / out opening 14a is in an open state, the preparation chamber 10 communicates with the outside. On the other hand, since the loading / unloading ports 14b and 14c are in a closed state, the processing chamber 11 does not communicate with either the preparation chamber 10 or the outside. Each of the preparation chamber 10 and the processing chamber 11 is connected to an exhaust system through a valve 15. A post-processing chamber (not shown) may be provided outside the carry-in / out port 14c.

  In this apparatus example, as shown in FIG. 1, the Mo plate 3 on which the sintered magnet body 1 is placed can move on the conveyor 13 from the left side to the right side in the figure. The member used for mounting the sintered magnet body 1 is not limited to the Mo plate, and may be formed from other high melting point materials (for example, heat resistant ceramics). Also, the member shape need not be plate-like, and may be another shape (for example, a wing shape). In the processing chamber 11, the RH bulk body 2 is disposed so as to face the sintered magnet body 1.

  The interiors of the preparation chamber 10 and the processing chamber 11 are each heated by a heater (not shown). For this reason, portions of the preparation chamber 10 and the processing chamber 11 that are heated to a high temperature are all made of a high melting point material.

  The sintered magnet body 1 placed stationary on the Mo plate 3 is carried into the preparation chamber 10 by the conveyor 13 via the carry-in / out port 14a. In the preparation chamber 10, the temperature and atmospheric pressure of the sintered magnet body 1 can be adjusted. Preferred values of temperature and atmospheric pressure will be described later. The sintered magnet body 1 is carried into the processing chamber 11 through the carry-in / out port 14 b while being left stationary on the Mo plate 3. As shown in FIG. 2, the sintered magnet body 1 in the processing chamber 11 is opposed to the RH bulk bodies 2 disposed on both sides of the conveyor 13 with a predetermined interval and is held for a predetermined time. After the predetermined time has elapsed, the sintered magnet body 1 may return to the preparation chamber 10 via the carry-in / out port 14b, or may be carried out to the outside through the carry-in / out port 14c.

  In this specification, “the sintered magnet body is carried out from the processing chamber” means that the sintered magnet body is carried out from the processing chamber in which the RH bulk body is installed, and is not necessarily from the entire processing apparatus. It does not mean that it is carried outside. That is, the case where the processing chamber 11 is returned to the preparation chamber 10 shown in FIGS. 1 and 2 or the case where the processing chamber 11 is unloaded (not shown) that can be installed outside the loading / unloading port 14c of the processing chamber 11 is included. And

  In addition, the arrangement configuration of the sintered magnet body 1 and the RH bulk body 2 in the processing chamber 11 is not limited to the above example, and is arbitrary. However, the structure which interrupts | blocks between the sintered magnet body 1 and the RH bulk body 2 should not be employ | adopted. The “opposite” in the present application means that the sintered magnet body and the RH bulk body face each other without being interrupted. In addition, “opposing arrangement” does not require that the main surfaces are arranged so as to be parallel to each other. Note that, for example, a net-like member made of a refractory metal may be disposed between the sintered magnet body 1 and the RH bulk body 2. This is because such a member does not “block” the heavy rare earth element RH vaporized or sublimated from the RH bulk body 2 from moving to the surface of the sintered magnet body 1.

  1 and 2 show a continuous furnace in which the two chambers of the preparation chamber 10 and the processing chamber 11 are connected laterally and the sintered magnet body 1 moves horizontally. There is no limitation, and a continuous furnace in which the two chambers of the preparation chamber 10 and the processing chamber 11 are connected in the vertical direction and the sintered magnet body 1 moves vertically may be used.

  In the present invention, first, the RH bulk body 2 is disposed in the processing chamber 11, and the processing chamber 11 is heated by a heating device (not shown), thereby raising the ambient temperature of the processing chamber 11. At this time, the atmospheric temperature of the processing chamber 11 is adjusted to a range of, for example, 700 ° C. to 1100 ° C., preferably 850 ° C. to 1000 ° C. The temperature of the RH bulk body also rises as the atmosphere temperature in the processing chamber increases, and soon reaches the temperature range. In this temperature region, the vapor pressure of the heavy rare earth metal RH is very small and hardly vaporizes, and the vapor of the heavy rare earth metal RH cannot be saturated in the processing chamber 11. According to the conventional technical common sense, in such a temperature range, it was considered that the heavy rare earth element RH evaporated from the RH bulk body 2 could not be supplied to the surface of the sintered magnet body 1 to form a film. .

  However, the present inventor can generate a slight amount of RH vapor in the vicinity of the RH bulk body 2 even in the temperature range, and without bringing the sintered magnet body 1 and the RH bulk body 2 into contact with each other. By arranging them close to each other, it is possible to deposit heavy rare earth metal on the surface of the sintered magnet body 1 at a low rate of several μm per hour (for example, 0.5 to 5 μm / Hr). By adjusting the temperature of 1 within an appropriate temperature range equal to or higher than the temperature of the RH bulk body 2, the heavy rare earth metal RH deposited from the gas phase is diffused deeply into the sintered magnet body 1 as it is. I found out that I could make it. This temperature range is a preferable temperature range in which the RH metal diffuses inward through the grain boundary phase of the sintered magnet body 1, and the slow precipitation of the RH metal and the rapid diffusion into the magnet body are efficient. Will be done.

  In the present invention, the RH slightly vaporized as described above is deposited on the surface of the sintered magnet body at a low rate, so that the temperature in the processing chamber is increased to a high temperature exceeding 1100 ° C. as in the case of RH precipitation by conventional vapor deposition. There is no need to heat the substrate, to apply a voltage to the sintered magnet body or the RH bulk body, or to set the entire processing chamber to an RH vapor atmosphere.

  In the present invention, as described above, the heavy rare earth element RH flying on the surface of the sintered magnet body is quickly diffused into the magnet body while suppressing vaporization (sublimation) of the RH bulk body. For this purpose, the temperature of the RH bulk body 2 is set in the range of 700 ° C. or more and 1100 ° C. or less, but the upper limit of the temperature range is preferably 1000 ° C. or less. The temperature of the sintered magnet body 1 is also preferably set in the range of 700 ° C. or more and 1100 ° C. or less, but may be room temperature to 700 ° C. when initially carried into the processing chamber 11. Also in this case, since the temperature of the sintered magnet body 1 rises while being held in the processing chamber 11, it is held in the processing chamber 11 within a range of 700 ° C. to 1100 ° C. for 10 minutes to 600 minutes. The temperature difference from the RH bulk body is preferably kept within 20 ° C.

  The distance between the sintered magnet body 1 and the RH bulk body 2 is preferably set to 0.1 mm to 300 mm. This interval is preferably 1 mm or more and 50 mm or less, more preferably 20 mm or less, and still more preferably 10 mm or less. As long as the state separated by such a distance can be maintained, the arrangement relationship between the sintered magnet body 1 and the RH bulk body 2 may be up and down or left and right.

  While the sintered magnet body 1 is held in the processing chamber 11, the sintered magnet body 1 may remain in one place, or may move slowly while maintaining the above-mentioned interval. Even in this case, it is preferable that the time during which the interval and temperature between the RH bulk body 2 and the sintered magnet body 1 are maintained within the above-described range is set in a range of 10 minutes to 600 minutes.

  After the predetermined time has elapsed, the sintered magnet body 1 may return to the original state from the carry-in / out port 14b, or it is carried out from the opposite-side carry-in / out port 14c to the opposite side. The processing may be carried out continuously as if it is carried in. Thus, productivity is improved if processing is performed continuously.

  In the illustrated example, the preparation chamber 10 is provided in front of the carry-in / out port 14b, and the temperature and atmospheric pressure of the sintered magnet body 1 can be adjusted. The temperature of the sintered magnet body 1 when being carried into the processing chamber 11 is preferably higher than the atmospheric temperature of the processing chamber 11 −100 ° C., more preferably higher than the atmospheric temperature −20 ° C. of the processing chamber 11. If the temperature of the sintered magnet body 1 is lower than the above, RH adheres more than necessary on the surface of the sintered magnet body 1 due to the temperature difference, and the RH is preferentially placed inside the magnet rather than being deposited on the surface of the magnet body. This is because the advantage of the present invention of diffusing becomes difficult to achieve. In addition, by adjusting the atmospheric pressure in the preparation chamber 10, it is possible to prevent the atmosphere from flowing in and out during loading and unloading.

  Further, a post-treatment chamber (not shown) may be provided after the carry-in / out port 14c, and after the sintered magnet body 1 is carried out, additional heat treatment, cooling, and aging treatment described later may be performed in the treatment chamber.

  Further, since the vaporized RH forms a uniform RH atmosphere as long as it is within the distance range as described above, the areas of the facing surfaces are not limited, and the surfaces of the narrowest areas may be facing each other. . According to the inventor's study, it is found that when an RH bulk body is installed perpendicular to the magnetization direction (c-axis direction) of the sintered magnet body 1, RH diffuses most efficiently into the sintered magnet body 1. It was. This is presumably because the diffusion rate in the magnetization direction is larger than the diffusion rate in the vertical direction when RH diffuses inward through the grain boundary phase of the sintered magnet body 1. The reason why the diffusion rate in the magnetization direction is larger than the diffusion rate in the perpendicular direction is presumed to be due to the difference in anisotropy due to the crystal structure.

  In the case of conventional vapor deposition equipment, the mechanism around the vapor deposition material supply part becomes an obstacle, and it is necessary to irradiate the vapor deposition material supply part with an electron beam or ions. It was necessary to provide a distance. For this reason, unlike the present invention, the vapor deposition material supply portion (RH bulk body 2) has not been disposed close to the object to be processed (sintered magnet body 1). As a result, it has been considered that the vapor deposition material cannot be sufficiently supplied onto the object to be processed unless the vapor deposition material is heated to a sufficiently high temperature and sufficiently vaporized. On the other hand, in this invention, the special mechanism for vaporizing (sublimating) vapor deposition material is not required, but RH metal can be deposited on the magnet surface by controlling the temperature of the whole processing chamber.

  Further, in the present invention, although the amount of RH metal vaporized is small, the sintered magnet body 1 and the RH bulk body 2 are arranged in a non-contact and close distance, so that the vaporized RH metal is efficiently applied to the surface of the sintered magnet body. It precipitates well and does not adhere to the wall surface in the processing chamber. Furthermore, if the wall surface in the processing chamber is made of a material that does not react with RH, such as a heat-resistant alloy such as Nb or ceramics, the RH metal adhering to the wall surface is vaporized again and finally deposited on the surface of the sintered magnet body. . For this reason, useless consumption of the heavy rare earth element RH which is a valuable resource can be suppressed.

  In the processing temperature range of the diffusion process performed in the present invention, the RH bulk body is hardly melted and softened, and the RH metal is vaporized (sublimated) from the surface, so that there is no significant change in the external shape of the RH bulk body in one processing process. It does not occur and can be used repeatedly. Moreover, since a large-scale apparatus is not required, a general vacuum heat treatment furnace can be used, and an increase in manufacturing cost can be avoided, which is practical.

The inside of the treatment chamber during the heat treatment is preferably an inert atmosphere. The “inert atmosphere” in this specification includes a vacuum or a state filled with an inert gas. Further, the “inert gas” is a rare gas such as argon (Ar), for example, but if it is a gas that does not chemically react between the RH bulk body and the sintered magnet body, the “inert gas” is designated as “inert gas”. May be included. The pressure of the inert gas is reduced to show a value lower than the atmospheric pressure. If the atmospheric pressure in the processing chamber is close to atmospheric pressure, it becomes difficult to supply RH metal from the RH bulk body to the surface of the sintered magnet body, but the amount of diffusion is controlled by the diffusion rate from the magnet surface to the inside, so The atmospheric pressure in the room is, for example, 10 ² Pa or less, and even if the atmospheric pressure in the processing chamber is further reduced, the diffusion amount of RH metal (coercivity improvement degree) is not greatly affected. The amount of diffusion is more sensitive to the temperature of the sintered magnet body than to the pressure.

The RH metal that has come to the surface of the sintered magnet body and has been deposited diffuses in the grain boundary phase toward the inside of the magnet using the difference between the heat of the atmosphere and the RH concentration at the magnet interface as a driving force. At this time, a part of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is replaced by the heavy rare earth element RH diffused and penetrated from the magnet surface. As a result, a layer enriched with heavy rare earth elements RH is formed in the outer shell of the R ₂ Fe ₁₄ B phase.

By forming such an RH enriched layer, the magnetocrystalline anisotropy of the outer shell portion of the main phase is increased and the coercive force H _cJ is improved. That is, the use of low RH metal, since the heavy rare-earth element RH to the deep internal magnet is diffused osmosis, to form efficiently RH concentrated layer on the outer periphery of the main phase, the decrease in remanence B _r It is possible to improve the coercive force H _cJ over the entire magnet while suppressing it.

According to the prior art, the speed at which the heavy rare earth element RH such as Dy is deposited on the surface of the sintered magnet body (film growth rate) is the speed at which the heavy rare earth element RH diffuses into the sintered magnet body ( Compared to the diffusion rate). For this reason, after forming an RH film having a thickness of several μm or more on the surface of the sintered magnet body, the heavy rare earth element RH diffuses from the RH film into the sintered magnet body. The heavy rare earth element RH supplied from the RH film that is not a gas phase but a solid phase diffuses not only in the grain boundary but also in the grain within the main phase located in the surface layer region of the sintered magnet body. The residual magnetic flux density _Br was lowered. The region in which the heavy rare earth element RH diffuses within the main phase and the difference in the RH concentration between the main phase and the grain boundary phase is limited to the surface layer region (for example, 100 μm or less in thickness) of the sintered magnet body. However, when the thickness of the entire magnet is thin, a decrease in the residual magnetic flux density _Br cannot be avoided.

  However, according to the present invention, the heavy rare earth element RH such as Dy supplied from the gas phase rapidly diffuses into the sintered magnet body after colliding with the surface of the sintered magnet body. This means that the heavy rare earth element RH penetrates deeply into the sintered magnet body through the grain boundary phase at a higher diffusion rate before diffusing into the main phase located in the surface layer region. Yes.

According to the present invention, in the surface layer region from the surface of the sintered magnet body to a depth of 100 μm, the concentration of the heavy rare earth element RH in the central portion of the R ₂ Fe ₁₄ B type compound crystal grains, and the R ₂ Fe ₁₄ B type compound There is a difference of 1 atomic% or more between the concentration of the heavy rare earth element RH in the grain boundary phase of the crystal grains. To suppress the decrease in remanence B _r, it is preferable to form the concentration difference of 2 atomic%.

Moreover, it is preferable to set the content of diffusing RH in the range of 0.05% to 1.5% in terms of the weight ratio of the whole magnet. Exceeds 1.5%, may not be able to suppress a decrease in remanence B _r, it is less than 0.1%, the effect of improving the coercive force H _cJ is small. A diffusion amount of 0.1% to 1% can be achieved by heat treatment for 10 to 180 minutes in the above temperature range and pressure. The processing time means a time in which the temperature of the RH bulk body and the sintered magnet body is 700 ° C. or more and 1100 ° C. or less and the pressure is 10 ⁻⁵ Pa or more and 500 Pa or less, and is always kept constant at a specific temperature and pressure. It does not represent only time.

  The surface state of the sintered magnet is preferably closer to a metallic state so that RH can easily diffuse and penetrate, and it is better to perform an activation treatment such as acid cleaning or blasting in advance. A dry process such as a plasma process may be performed in the preparation chamber 10. However, in the present invention, when the heavy rare earth element RH is vaporized and deposited on the surface of the sintered magnet body in an active state, it diffuses into the sintered magnet body at a higher rate than the formation of a solid layer. Go. For this reason, the surface of the sintered magnet body may be in a state where oxidation has progressed, for example, after the sintering process or after the cutting process is completed.

  According to the present invention, since the heavy rare earth element RH can be diffused mainly through the grain boundary phase, the heavy rare earth element RH is efficiently diffused to a deeper position inside the magnet by adjusting the processing time. It is possible.

  The shape and size of the RH bulk body are not particularly limited, and may be a plate shape or an indefinite shape (a stone shape). A large number of micropores (diameter of about 10 μm) may exist in the RH bulk body. The RH bulk body is preferably formed of an RH metal containing at least one heavy rare earth element RH or an alloy containing RH. Moreover, the higher the vapor pressure of the material of the RH bulk body, the greater the amount of RH introduced per unit time, which is more efficient. Vapor pressure of oxides, fluorides, nitrides, and the like containing heavy rare earth elements RH is extremely low, and almost no vapor diffusion occurs within this range of conditions (temperature, degree of vacuum). For this reason, even if the RH bulk body is formed from an oxide, fluoride, nitride, or the like containing the heavy rare earth element RH, the effect of improving the coercive force cannot be obtained.

According to the present invention, for example, even for a thickness of 3mm or more thick material magnet, increasing both the remanence B _r and coercivity H _cJ with the heavy rare-earth element RH in small amounts, the magnetic properties at high temperatures It is possible to provide a high performance magnet that does not deteriorate. Such a high-performance magnet greatly contributes to the realization of an ultra-small and high-power motor. The effect of the present invention using the grain boundary diffusion is particularly remarkable in a magnet having a thickness of 10 mm or less.

In the present invention, the heavy rare earth element RH may be diffused and penetrated from the entire surface of the sintered magnet body, or the heavy rare earth element RH may be diffused and penetrated from a part of the surface of the sintered magnet body. In order to diffuse and infiltrate RH from a part of the surface of the sintered magnet body, for example, by masking a portion of the sintered magnet body that does not want to diffuse and infiltrate RH, heat treatment can be performed in the same manner as described above. Good. According to such a method, a magnet having a _partially improved coercive force H _cJ can be obtained.

When additional heat treatment is performed on the magnet that has undergone the vapor deposition diffusion process of the present invention, the coercive force (H _cJ ) can be further improved. Conditions for the additional heat treatment (treatment temperature, time) may be the same conditions as the vapor deposition diffusion conditions, and it is preferable to hold the temperature at 700 ° C. to 1100 ° C. for 10 minutes to 600 minutes.

The additional heat treatment will be described with reference to the example shown in FIGS. 1 and 2, for example, after the diffusion step, the Ar partial pressure in the processing chamber 11 is increased to about 10 ³ Pa so as not to evaporate the heavy rare earth element RH, and the heat treatment is performed as it is. It is also possible to carry out heat treatment under the above-mentioned conditions by moving from the carry-in / out port 14c to a post-treatment chamber (not shown).

  Since the mechanical strength such as the bending strength in the sintered magnet body is improved by performing vapor deposition diffusion, it is practically preferable. This is because, during vapor deposition diffusion, the strain inherent in the sintered magnet body is released, the work-degraded layer is recovered, or the heavy rare earth element RH is diffused, so that the main phase and the grain boundary phase are dispersed. This is presumed to be a result of improved crystal matching. When the crystal matching between the main phase and the grain boundary phase is improved, the grain boundary is strengthened and the resistance against grain boundary fracture is improved.

  Hereinafter, a preferred embodiment of a method for producing an R—Fe—B rare earth sintered magnet according to the present invention will be described.

(Embodiment 1)
[Raw material alloy]
First, an alloy containing 25 to 40% by mass of a light rare earth element RL, 0.6 to 1.6% by mass of B (boron), the remainder Fe and inevitable impurities is prepared. A part of B may be substituted by C (carbon), and a part of Fe (50 atomic% or less) may be substituted by another transition metal element (for example, Co or Ni). This alloy is suitable for a variety of purposes, including Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and About 0.01 to 1.0% by mass of at least one additive element M selected from the group consisting of Bi may be contained.

  The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy by a strip casting method will be described.

  First, a raw material alloy having the above composition is melted by high frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy slab having a thickness of about 0.3 mm. The alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm, for example, before the next hydrogen pulverization. In addition, the manufacturing method of the raw material alloy by a strip cast method is disclosed by US Patent 5,383,978 specification, for example.

[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement treatment (hereinafter sometimes referred to as “hydrogen pulverization treatment”) step is performed inside the hydrogen furnace. When the coarsely pulverized alloy powder after hydrogen pulverization is taken out from the hydrogen furnace, it is preferable to perform the take-out operation in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. By doing so, it is possible to prevent the coarsely pulverized powder from oxidizing and generating heat, and to suppress the deterioration of the magnetic properties of the magnet.

  By the hydrogen pulverization, the rare earth alloy is pulverized to a size of about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After hydrogen pulverization, the embrittled raw material alloy is preferably crushed more finely and cooled. When the raw material is taken out in a relatively high temperature state, the cooling process time may be relatively long.

[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. Thus, a fine powder of about 0.1 to 20 μm (typically 3 to 5 μm) can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.

[Press molding]
In the present embodiment, for example, 0.3 wt% of a lubricant is added to and mixed with the magnetic powder produced by the above method in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. Next, the magnetic powder produced by the above-described method is molded in an orientation magnetic field using a known press machine. The intensity of the applied magnetic field is, for example, 1.5 to 1.7 Tesla (T). The molding pressure is set so that the green density of the molded body is, for example, about 4 to 4.5 g / cm ³ .

[Sintering process]
With respect to said powder molded object, the process hold | maintained for 10 to 240 minutes at the temperature within the range of 650-1000 degreeC, and sintering further by the temperature (for example, 1000-1200 degreeC) higher than said holding temperature after that. It is preferable to sequentially perform the proceeding steps. During sintering, particularly when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Then, sintering progresses and a sintered magnet body is formed. As described above, since the vapor deposition diffusion treatment can be performed even when the surface of the sintered magnet body is oxidized, aging treatment (400 ° C. to 700 ° C.) and grinding for dimension adjustment are performed after the sintering step. May be.

[Vapor deposition diffusion process]
Next, the rare earth element RH is efficiently diffused and infiltrated into the sintered magnet body thus manufactured to improve the coercive force H _cJ . Specifically, for example, by arranging and heating an RH bulk body containing a heavy rare earth element RH in the processing chamber shown in FIGS. 1 and 2, an RH vapor atmosphere is formed at least in the vicinity of the RH bulk body, and then sintered. By bringing the magnet body into the processing chamber and arranging the magnet body so as to face the RH bulk body, the heavy rare earth element RH is supplied from the RH bulk body to the surface of the sintered magnet body and diffused into the sintered magnet body.

  In the diffusion step in the present embodiment, the temperature of the sintered magnet body is preferably set to be equal to or higher than the temperature of the bulk body before being carried into the processing chamber, but it is room temperature to 700 ° C. before being carried in. It is preferable that the temperature of the sintered magnet body, which has been a temperature, rises rapidly in the processing chamber and is maintained at or above the temperature of the bulk body. Here, the temperature of the sintered magnet body being the same as the temperature of the bulk body means that the temperature difference between them is within 20 ° C. Specifically, it is preferable to set the temperature of the RH bulk body in the range of 700 ° C. or more and 1100 ° C. or less, and the temperature of the sintered magnet body in the range of 700 ° C. or more and 1100 ° C. or less. Further, as described above, the interval between the sintered magnet body and the RH bulk body is set to 0.1 mm to 300 mm, preferably 3 mm to 100 mm, more preferably 4 mm to 50 mm.

  In a preferred embodiment of the present invention, the thickness of the RH film deposited on the surface of the sintered magnet body can be suppressed to, for example, 1 μm or less immediately after the heavy rare earth element RH film is deposited. This is because the growth rate of the RH film can be suppressed by setting the temperature of the RH bulk body in the processing chamber to be relatively low. Moreover, since the diffusion of the heavy rare earth element RH can be promoted by heating the sintered magnet body introduced into the processing chamber in advance, the heavy rare earth element RH flying on the surface of the sintered magnet body is put inside the magnet body. It can be diffused quickly. As a result, the RH film is not deposited thick on the surface of the magnet body, and useless use of the heavy rare earth element RH film can be avoided. Even immediately after the deposition of the heavy rare earth element RH film, a part of the light rare earth element RL is replaced by the heavy rare earth element RH, so that it is necessary to perform additional heat treatment for diffusion thereafter. Not particularly.

When the pressure of the atmospheric gas during the vapor deposition diffusion step is 10 ^{−5 to} 500 Pa, vaporization (sublimation) of the RH bulk body appropriately proceeds and vapor deposition diffusion treatment can be performed. In order to efficiently perform the vapor deposition diffusion treatment, it is preferable to set the pressure of the atmospheric gas within a range of 10 ^{−3 to 1} Pa. The temperature of the RH bulk body and the sintered magnet body is in the range of 700 ° C. or higher and 1100 ° C. or lower, and the time for maintaining the distance between the sintered magnet body and the RH bulk body at 0.1 mm to 300 mm is 10 minutes to 600 minutes. It is preferable to set in the range. However, the holding time is such that the temperature of the RH bulk body and the sintered magnet body is 700 ° C. or more and 1100 ° C. or less, the interval between the sintered magnet body and the RH bulk body is 0.1 mm to 300 mm, and the pressure is 10 ⁻⁵ Pa or more and 500 Pa or less. It does not necessarily represent only the time that is held constant at a specific temperature, interval, and pressure.

  The diffusion process in this embodiment is not sensitive to the surface condition of the sintered magnet body, and a film made of Al, Zn, or Sn may be formed on the surface of the sintered magnet body before the diffusion process. This is because Al, Zn, and Sn are low melting point metals, and if they are in a small amount, they do not deteriorate the magnet characteristics and do not hinder the diffusion described above. Note that the bulk body does not have to be composed of one kind of element, but the heavy rare earth element RH and the element X (Nd, Pr, La, Ce, Al, Zn, Sn, Cu, Co, Fe, Ag, and It may contain at least one kind of alloy selected from the group consisting of In. Since such an element X lowers the melting point of the grain boundary phase, the effect of promoting the grain boundary diffusion of the heavy rare earth element RH can be expected. By performing vacuum heat treatment in such a state that the bulk body of such an alloy and the Nd sintered magnet are spaced apart from each other, the heavy rare earth element RH and the element X are deposited on the magnet surface, and the liquid phase is preferentially formed. It can be diffused into the magnet through the field phase (Nd rich phase).

  Further, during the heat treatment for diffusion, Nd and Pr in the grain boundary phase are vaporized with a slight amount. Therefore, if the element X is Nd and / or Pr, the evaporated Nd and / or Pr can be supplemented, which is preferable.

  After the diffusion treatment, the above-described additional heat treatment (700 ° C. to 1100 ° C.) may be performed. Moreover, although an aging treatment (400 degreeC-700 degreeC) is performed as needed, when performing additional heat processing (700 degreeC-1100 degreeC), it is preferable to perform an aging treatment after that. The additional heat treatment and the aging treatment may be performed in the same processing chamber.

  Practically, it is preferable to subject the sintered magnet body after vapor deposition diffusion to surface treatment. The surface treatment may be a known surface treatment, and for example, a surface treatment such as Al deposition, electric Ni plating, resin coating, or the like can be performed. Prior to the surface treatment, a known pretreatment such as sandblasting, barrel treatment, etching treatment or mechanical grinding may be performed.

  Moreover, you may perform the grinding for dimension adjustment after a diffusion process. Even if it goes through such a process, the coercive force improvement effect hardly changes. The grinding amount for dimensional adjustment is 1 to 300 μm, more preferably 5 to 100 μm, and still more preferably 10 to 30 μm.

  First, an alloy blended so as to have a composition of Nd: 32.0, B: 1.0, Co: 0.9, Cu: 0.1, Al: 0.2, and the balance: Fe (% by mass) is used. Then, an alloy flake having a thickness of 0.2 to 0.3 mm was produced by a strip casting method.

  Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with a hydrogen gas atmosphere having a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.

  After adding 0.05 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the hydrogen treatment described above and mixing, a pulverization step using a jet mill device is performed, so that the powder particle size is about 3 μm. A powder was prepared.

  The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus and subjected to a sintering process at 1020 ° C. for 4 hours in a vacuum furnace. Thus, after producing a sintered body block, this sintered body block was mechanically processed to obtain a sintered magnet body having a thickness of 5 mm (magnetization direction) × length 7 mm × width 7 mm.

The sintered magnet body is pickled with a 0.3% nitric acid aqueous solution, dried, and then placed on the Mo plate 3 shown in FIG. 1 in the preparation chamber 10 having the configuration shown in FIGS. 1 and 2. The temperature was raised while evacuating to 900 ° C. and an atmosphere of 1 × 10 ⁻² Pa. After the temperature of the sintered magnet body reached 900 ° C., it was held for 120 minutes.

On both sides of the conveyor 13 in the processing chamber 11, to place the RH bulk body of the size of 30 mm × 50 mm × 5 mm is formed from 99.9% pure Dy, 900 ° C. The processing chamber 11, 1 × 10 ^-2 Pa The atmosphere was set. The shutter of the carry-in / out port 14b was opened, and the sintered magnet body was carried into the processing chamber 11 by the conveyor 13 in a state where the sintered magnet body was left on the Mo plate 3. The interval between the sintered magnet body and the RH bulk body was set to 10 mm.

After carrying the sintered magnet body into the processing chamber 11, the sintered magnet body was held at 900 ° C. and 1 × 10 ⁻² Pa for 120 minutes. After the holding, Ar was introduced into the processing chamber 11 and cooled. The sintered magnet body after cooling was subjected to aging heat treatment at 500 ° C. and 2 Pa for 120 minutes, and then the magnet characteristics were measured with a BH tracer (Sample 1).

  Samples 2 to 8 were obtained in the same manner as Sample 1 except that the conditions in the preparation chamber 10 and the processing chamber 11 were changed. Sample 0 is a comparative example in which vapor deposition diffusion was not performed. Table 1 shows the results of processing conditions and magnet characteristics. Unless otherwise indicated, the temperature in the table means the sintered magnet body temperature. This temperature is approximately equal to the temperature of the RH bulk body.

Under the conditions of Samples 1 and 10 to 12, the temperature of the sintered magnet body was raised to the same temperature (900 ° C. or 850 ° C.) as the atmosphere temperature of the processing chamber 11 in the preparation chamber 10, and then the sintered magnet body was processed into the processing chamber 11. Dy deposition and diffusion occurred efficiently, and the coercive force (H _cJ ) was greatly improved without substantially reducing the residual magnetic flux density (B _r ).

Under the conditions of Sample 2, the temperature of the sintered magnet body when it is carried into the processing chamber 11 is room temperature (20 ° C.), and the atmosphere of the processing chamber 11 at the beginning when the sintered magnet body is carried into the processing chamber 11 ( Due to the temperature difference from the atmosphere near the RH bulk body), Dy is abruptly deposited on the surface, and then the diffusion to the grain boundary proceeds as the magnet temperature rises. The decrease in _r is estimated to have increased somewhat.

In Samples 3 and 4, the atmospheric temperature of the processing chamber 11 is as high as 1150 ° C., so the evaporation amount (vapor pressure) of Dy is large, and at such high temperatures, intragranular diffusion into the main phase crystal grains of the magnet is extremely large. to proceed, although H _cJ is improved greatly, decrease in B _r is significant.

In Samples 5 to 8, since the atmospheric temperature of the processing chamber 11 is as low as 650 ° C., Dy vapor deposition diffusion hardly occurs and the coercive force H _cJ hardly increases or is very small.

For samples 9 treatment time is 7 minutes and shorter, Dy vapor diffusion hardly occurs, or improving the coercive force H _cJ hardly occurs, very small.

  In the present invention, an R—Fe—B rare earth sintered magnet with improved coercive force can be obtained with almost no decrease in residual magnetic flux density, and therefore, it can be suitably used in technical fields such as various electronic devices and motors. obtain. Moreover, since the heavy rare earth element RH can be effectively utilized and the amount of use thereof can be reduced, it is possible to protect rare resources.

It is sectional drawing which shows one structural example of the vapor deposition diffusion apparatus which can be used suitably by this invention. It is a figure which shows the plane structural example of the vapor deposition diffusion apparatus which can be used suitably by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sintered magnet body 2 RH bulk body 3 Mo board 10 Preparation chamber 11 Processing chamber 13 Conveyor 14a Carrying in / out port 14b Carrying in / out port 14c Carrying in / out port 15 Valve

Claims (8)

By placing a bulk body containing a heavy rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) in a processing chamber, and heating the processing chamber to 700 ° C. or higher and 1100 ° C. or lower, A step (A) of forming an RH vapor atmosphere at least near the bulk body in a processing chamber;
A step (B) of carrying an R—Fe—B rare earth sintered magnet body into the processing chamber;
The R—Fe—B rare earth sintered magnet body is placed opposite to the bulk body and held for 10 minutes to 600 minutes, whereby the heavy rare earth element RH is retained in the R—Fe—B rare earth sintered body. A step (C) of diffusing the heavy rare earth element RH into the R-Fe-B rare earth sintered magnet body while supplying the surface to the surface of the magnet body. R-Fe-B rare earth sintered magnet Manufacturing method.   2. The R—Fe according to claim 1, wherein in the step (C), an average interval between the bulk body and the R—Fe—B rare earth sintered magnet body is set within a range of 0.1 mm to 300 mm. -Manufacturing method of B type rare earth sintered magnet.   The said process (C) WHEREIN: R of Claim 1 which hold | maintains the temperature of the said bulk body and the said R-Fe-B type rare earth sintered magnet body in the range of 700 degreeC or more and 1100 degrees C or less for 10 minutes-600 minutes. -Manufacturing method of Fe-B rare earth sintered magnet. 2. The method for producing an R—Fe—B rare earth sintered magnet according to claim 1, wherein in the step (C), the pressure of the atmospheric gas in the processing chamber is adjusted within a range of 10 ^{−5 to} 500 Pa. 3.   In the step (C), the temperature difference between the temperature of the R-Fe-B rare earth sintered magnet body and the temperature of the bulk body is maintained within 20 ° C for 10 minutes to 600 minutes. The manufacturing method of the R-Fe-B type rare earth sintered magnet of description.   The method for producing an R-Fe-B rare earth sintered magnet according to claim 5, wherein a step of heating the R-Fe-B rare earth sintered magnet body in advance is performed before performing the step (B).   An R—Fe—B based rare earth sintered magnet produced by the production method according to claim 1. R-Fe-B rare earth sintered magnet body containing light rare earth element RL (at least one of Nd and Pr) as the main rare earth element R, and deposited on the surface of the R-Fe-B rare earth sintered magnet body A rare earth element RH (at least one selected from the group consisting of Dy, Ho, and Tb) film, and an R—Fe—B based rare earth sintered magnet in production
Immediately after the deposition of the heavy rare earth element RH film, the thickness of the film is 1 μm or less, and a part of the light rare earth element RL is replaced by the heavy rare earth element RH. Rare earth sintered magnet.

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